Translating SQL Queries into Relational Algebra
- Query optimization started out as a set of heuristics:
A set of transformations that seem like a good idea. E.g.,
always push select below join.
- A much better approach is cost-based optimization.
- For a "large" query, the set of possible execution plans is
far too big to consider each one.
- So there is still some use of heuristics.
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